Structural characterization of semi-heusler/light metal composites prepared by spark plasma sintering

Jaromír Kopeček,Jaroslava Nováková,Oleg Heczko,Miloš Janeček,Přemysl Beran,Pavel Novák,Vasyl Ryukhtin,Michal Landa,Tomáš Chráska,Zdeněk Pala,Radek Mušálek,Pavel Strunz,Hanuš Seiner,Kristína Bartha,Josef Stráský

doi:10.1038/s41598-018-29479-3

Abstract

A composite of powders of semi-Heusler ferromagnetic shape memory and pure titanium was successfully prepared by spark plasma sintering at the temperature of 950 °C. Sintering resulted in the formation of small precipitates and intermetallic phases at the heterogeneous interfaces. Various complementary experimental methods were used to fully characterize the microstructure. Imaging methods including transmission and scanning electron microscopy with energy dispersive X-ray spectroscopy revealed a position and chemical composition of individual intermetallic phases and precipitates. The crystalline structure of the phases was examined by a joint refinement of X-ray and neutron diffraction patterns. It was found that Co38Ni33Al29 decomposes into the B2-(Co,Ni)Al matrix and A1-(Co,Ni,Al) particles during sintering, while Al, Co and Ni diffuse into Ti forming an eutectic two phase structure with C9-Ti2(Co,Ni) precipitates. Complicated interface intermetallic structure containing C9-Ti2(Co,Ni), B2-(Co,Ni)Ti and L21-(Co,Ni)(Al,Ti) was completely revealed. In addition, C9-Ti2(Co,Ni) and A1-(Co,Ni,Al) precipitates were investigated by an advanced method of small angle neutron scattering. This study proves that powder metallurgy followed by spark plasma sintering is an appropriate technique to prepare bulk composites from very dissimilar materials.

Highlights

A composite of powders of semi-Heusler ferromagnetic shape memory and pure titanium was successfully prepared by spark plasma sintering at the temperature of 950 °C
The effect of spark plasma sintering on microstructure, phase composition and thermoelectric properties of a half-Heusler compound were investigated in few previous studies[16,17,18], but these researches did not exploit the ability of spark-plasma sintering (SPS) for sintering materials mixtures
Spark plasma sintering method was successfully used to prepare dense composite of a light-weight metal and shape memory alloy (Co38Ni33Al29) and its structure was investigated by a broad variety of microscopic and diffraction techniques

Summary

Introduction

A composite of powders of semi-Heusler ferromagnetic shape memory and pure titanium was successfully prepared by spark plasma sintering at the temperature of 950 °C. The effort to combine materials with very dissimilar physical and mechanical properties into a compact composite structure may encounter considerable technical issues, especially when the characteristic length in the composite is required to appear at the scale of micrometers or even nanometers Both Nature and advanced technologies are capable of producing such materials. The effect of spark plasma sintering on microstructure, phase composition and thermoelectric properties of a half-Heusler compound were investigated in few previous studies[16,17,18], but these researches did not exploit the ability of SPS for sintering materials mixtures. In the case of sintering of very dissimilar materials, the interface phases, which affect resulting physical properties, are likely to occur As a consequence, it can be extremely difficult and complicated to characterize properly and completely these interface layers

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